Causes for different spatial distributions of minimum Arctic sea-ice extent in 2007 and 2012
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摘要: 卫星数据显示北极海冰范围(SIE)最小值出现在2012年9月份,其次是2007年9月份,但这两年融冰的空间分布有显著差异。本文通过分析夏季大气环流模态和海洋上层状态,解释这两年北极海冰空间分布不同的原因。利用北冰洋存在的冰-温和冰-汽正反馈机制,结果显示2007和2012年较高表面气温(SAT)和海平面气压(SAT)会伴随着更多的表面水汽(SH)和更高的海表面温度(SST),因而,向极风加强促进这两年不同海域北极夏季海冰的融化。SAT是影响海冰融化的主要因素。秋季北极SIE异常和夏季北极SAT异常的相关系数超过-84%。SAT在2007和2012年夏季不同区域的增加导致北极海冰的快速融化;与SAT有直接关系的SLP以及相应的风场也是海冰融化的促进因素。向极风加强给极区带来暖湿气流加速2007和2012年夏季不同区域的海冰融化;伴随气温升高,空气中表面SH增加和SST升高促进这两年海冰在不同区域的融化,形成两种正反馈机制。Abstract: Satellite records show the minimum Arctic sea ice extents (SIEs) were observed in the Septembers of 2007 and 2012, but the spatial distributions of sea ice concentration reduction in these two years were quite different. Atmospheric circulation pattern and the upper-ocean state in summer were investigated to explain the difference. By employing the ice-temperature and ice-specific humidity (SH) positive feedbacks in the Arctic Ocean, this paper shows that in 2007 and 2012 the higher surface air temperature (SAT) and sea level pressure (SLP) accompanied by more surface SH and higher sea surface temperature (SST), as a consequence, the strengthened poleward wind was favorable for melting summer Arctic sea ice in different regions in these two years. SAT was the dominant factor influencing the distribution of Arctic sea ice melting. The correlation coefficient is -0.84 between SAT anomalies in summer and the Arctic SIE anomalies in autumn. The increase SAT in different regions in the summers of 2007 and 2012 corresponded to a quicker melting of sea ice in the Arctic. The SLP and related wind were promoting factors connected with SAT. Strengthening poleward winds brought warm moist air to the Arctic and accelerated the melting of sea ice in different regions in the summers of 2007 and 2012. Associated with the rising air temperature, the higher surface SH and SST also played a positive role in reducing summer Arctic sea ice in different regions in these two years, which form two positive feedbacks mechanism.
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Key words:
- Arctic sea ice extent /
- atmospheric circulation /
- upper-ocean feedback
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